Monzo builds a more robust and higher quality app with Compose

Monzo is a bank and app offering digital financial services. Their mission is to make money work for everyone. Monzo’s design system started to deviate from Material Design so they wanted an easy way to write and maintain custom components that are constantly evolving—so they chose Jetpack Compose.

What they did

With Compose the Material Design components are provided as a layer over the design-system-agnostic foundation APIs. Monzo used the foundation APIs to build their own component library, using the Material components as reference. They started by migrating a screen at a time, now using Compose in all new screens. Now, Compose is used in production, by all of the Android engineers: “We didn’t encounter any major problems, and so we felt confident enough to start using it for some select new features, and eventually for all new features.”


The Monzo team created components that enable them to easily build new screens: “The components we provide out of the box make building a screen while learning Compose a much smoother experience. The slot-based APIs is a fantastic pattern that makes it really easy for us to build larger components out of lots of small building blocks.“

With Compose, the Monzo team were able to build a higher quality app, adding delightful features that previously they couldn’t get to in their sprints: “One example is animations - they’re so easy to add in Compose that there’s very little reason not to animate things like color/size/elevation changes. These ‘nice to have’ animations are often too difficult to be worth the effort and complexity in the View system.”

Their code is now shorter, and it's easier to read, understand, and maintain: “Declarative code is much easier to reason about than code that manipulates a mutable UI hierarchy. It’s also much easier to trace through code when it’s all written in the same language and often the same file, rather than jumping back and forth between Kotlin and XML. Don’t even get me started on XML themes and styles! Theming is a lot easier to understand in Compose. Our theme only consists of the properties we define, the values are consistent across devices, and because it’s in Kotlin it is really easy to search and follow in the IDE.“

Compose allowed the Monzo team to easily test their app and ensure their app is accessible: “It’s helped us write tests that are less fragile, run reliably, and give us a lot of confidence that our app actually works in the hands of our users. Testing through the semantics system also ensures that our screens are at least reasonably accessible by default.”

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